Microsoft's share of shipped devices will climb slightly this year and pick up some steam in 2016, but Apple's share will grow at a more sluggish pace because of slow-downs in iPhone and iPad, Gartner forecast Monday.

For 2015, Windows' share of the operating systems on all devices -- smartphones, tablets, PCs, ultra-lights and hybrids -- will climb to 14.4 percent, up from 14 percent last year, Gartner said in new estimates. It claimed that shipments would increase by less than 7 percent, to 355 million.

As it did several times last year, Gartner downgraded Windows' numbers for 2015 Monday: Its October 2014 forecast pegged Windows at 14.6 percent by the end of this year.

Gartner projected Windows' share in 2016 would climb to 15.3 percent on the back of 396.3 million devices shipped, a year-over-year increase of almost 11 percent, the largest boost since 2013, when PC sales began a prolonged contraction.

Microsoft wasn't the only OS maker whose forecast worsened in Gartner's latest estimate. Apple will also grow its share at a slower tempo than anticipated by several predictions of 2014.

Apple finished 2014 with an operating system share of 11 percent by virtue of about 262.6 million devices shipped, said Gartner, and should see its slice of the OS pie grow to 11.3 percent in 2015. That's less than the 11.6 percent pegged in the October forecast.

The Cupertino, Calif. company's share will reach that 11.6 percent -- but now not until the end of 2016, Gartner said today.

Those numbers were significantly under the aggressive estimate Gartner touted a year ago; in January 2014, it predicted Apple's share would reach 13.9 percent in 2014 and a whopping 15.9 percent in 2016, hot on the heels of Windows.

They also represented year-over-year increases in devices shipped of 6 percent for this year and 7 percent for the next, the numbers in marked contrast to the double-digit growth Apple experienced in 2013 and 2014.

What happened to make Gartner change its prognostication tune?

Its analysts cited Apple's two largest-volume lines, the iPad and iPhone, for their change of heart, pointing -- like many other analysts have in 2014 -- to a longer-than-anticipated refresh cycle for Apple's tablet and the belief that Apple will find it tougher showing iPhone growth in the future as it runs low of new markets and has a difficult time topping the iPhone 6 line.

"The challenge for the next iPhone to find significant growth becomes greater [in 2015 and 2016]," Ranjit Atwal, a Gartner analyst, said in a statement.

Meanwhile, Gartner's forecast for Android got more bullish than ever on Monday. By the end of 2015, Android will have captured 58.9 percent of the device share -- up from an October 2014 forecast of 57.4 percent and a January 2014 bet of just 47.8 percent -- and will grow even larger in 2016, accounting for 62.9 percent of all smartphones and tablets in two years.

Data: Gartner

Shipments of Windows-powered devices -- personal computers, tablets, hybrids and smartphones -- will grow faster than those that rely on Apple's iOS and OS X through 2016.

This story, "Microsoft's device share growth to outpace Apple's through 2016" was originally published by
Computerworld.